Fatty acid-based materials (fatty materials) such as glyceride oils, wax esters, milk fat, and other fatty acid compounds have a long history of use since many of these materials are naturally derived from plants (e.g. vegetable oils) or animals (e.g. tallow, milk fat, etc.).
While these fatty materials often have been directly used in their crude state, modern commercial products based on these materials are typically subjected to a refining process. Refining processes may be used to remove various impurities which are undesirable for reasons of health, performance, aesthetics, etc.
The fatty material may contain impurities such as color bodies, chlorophyll, phospholipids (phosphatides), trace metals (e.g. Ca, Mg, Fe), free fatty acids (FFA), gums, soaps and/or other impurities. This variety of diverse impurities has led to the development of numerous refining processes involving particular combinations of chemical and/or physical treatment steps. A detailed review of refining processes may be found in the "Handbook for Soy Oil Processing and Utilization," ed. by David R. Erikson et al., ASA/AOCS Monograph, 1980.
Recently, new refining processes have been developed which share the common feature that an amorphous adsorbent is contacted with a soap-containing fatty material whereby soap and possibly other impurities in the fatty material are adsorbed by the amorphous adsorbent. Such refining processes are disclosed in European Patent Application 0247411 (EP '411--"MCR") and U.S. patent application Ser. No. 07/677455 (Ser. No. '455--"MPR"), filed Apr. 3, 1991. The disclosures of these applications are incorporated herein by reference.
In the EP '411 process, large amounts of soap are intentionally created in the fatty material by the addition of a chemical base (e.g. NaOH) to the fatty material at a point in the '411 process to eliminate free fatty acid and to facilitate removal of other impurities. The bulk of the soap is then separated from the fatty material by a primary centrifuge. The fatty material output from the primary centrifuge is then contacted with an amorphous adsorbent (e.g. a silica gel) to remove residual soaps and impurities from the fatty material. Immediately after the adsorption or at some point downstream in the process, the soap-containing adsorbent is separated from the fatty material. The fatty material may be subjected to additional refining steps (e.g. bleaching, deodorizing, etc.) before and/or after the separation of the amorphous adsorbent.
The Ser. No. '455 process differs from the EP '411 process by creating only a small amount of soap by addition of chemical base. The smaller amount of soap can be removed from the fatty material by simply contacting with amorphous adsorbent, i.e. without need for the primary centrifuge step. As with the EP '411 process, the fatty material may be subjected to additional refining steps before and/or after separation of the amorphous adsorbent.
A problem exists with these amorphous adsorbent-based processes if one tries to subject the fatty material to vacuum bleaching before removal of the soap-containing adsorbent. Namely, adsorbed soap appears to leach out of the amorphous adsorbent in the vacuum bleacher. This problem occurs even if the amount of soap initially created is decreased relative to the amount of amorphous adsorbent used. Soap leaching is undesirable since it causes sliming of packed beds and filters used in the refining process. Since commercial refining processes are typically continuous processes with large throughput, even concentrations of a few ppm of soap are generally unacceptable since the effect of the soap is magnified by the large throughput. Also, the presence of soap in the fatty material after vacuum bleaching can have adverse effects in subsequent processing steps.
To date, the only solution to this problem has been to separate out the soap-containing adsorbent prior to vacuum bleaching. However, the insertion of a filtration step before the vacuum bleacher may be commercially undesirable or difficult to install in an existing refining set up. Thus, there is a need for a way to overcome the soap leaching problem without resorting to filtration before vacuum bleaching.